Devices of this type are normally used, in combination with spring means, in movable members such as sliding drawers or hinged hatches. More specifically, such devices are designed in such a way that, in one direction of movement of the movable member to which they are fitted, they can exert a braking action on this movement, while they are substantially inactivated, and therefore do not have this braking action, in the opposite direction of movement. Dampers of this type are generally called one-way dampers. This arrangement is particularly useful if the rotary damper, fitted in combination with a spring, is positioned in such a way that it provides no braking action when the movable member is moved, by a user's hand for example, against the action of the spring and exerts this braking action when the movable member is left free to move under the elastic return force of the spring. Thus, in one direction of rotation, the braking action is not added to the force of the spring, and therefore does not impede the movement of the movable member, while in the other direction of rotation the braking action is opposed to the return force of the spring, making the movement of the movable member less abrupt.
In particular, examples of prior art devices are described in patent applications JP 9177857 A and JP 10184734 A. JP 9177857 A describes a rotary damper comprising a first component, a second component mounted on the first component so as to be rotatable about an axis of rotation, and a viscous braking fluid interposed between the first component and the second component in order to brake the rotation of the second component with respect to the first component. The damper also comprises a third component mounted on the second component so as to be rotatable about the axis of rotation, in such a way that the second and third components delimit between them a lateral support surface and a lateral shaft surface which is rotatable within the lateral support surface, a plurality of rolling elements being interposed between these surfaces.
The lateral shaft and support surfaces and the rolling elements are positioned in such a way that the third component can rotate freely with respect to the second component in a first direction of rotation of the lateral shaft surface with respect to the lateral support surface, while the third component is coupled rigidly to the second component in a second and opposite direction of rotation of the lateral shaft surface with respect to the lateral support surface. This is made possible by means of a race positioned between the second and third components of the rotary damper for housing the rolling elements, and by means of cam portions formed on the lateral support surface, one of these being provided at the position of each rolling element.
JP 10184734 A describes a rotary damper comprising a first component, a second component mounted on the first component so as to be rotatable about an axis of rotation, and a viscous braking fluid interposed between the first component and the second component in order to brake the rotation of the second component with respect to the first component. The damper also comprises a third component mounted on the second component so as to be rotatable about the axis of rotation, in such a way that the second and third components delimit between them a lateral support surface and a lateral shaft surface which is rotatable within the lateral support surface, a plurality of rolling elements being interposed between these surfaces. The lateral shaft and support surfaces and the rolling elements are positioned in such a way that the third component can rotate freely with respect to the second component in a first direction of rotation of the lateral shaft surface with respect to the lateral support surface, while the third component is coupled rigidly to the second component in a second and opposite direction of rotation of the lateral shaft surface with respect to the lateral support surface. This is made possible by means of shaped recesses formed on the lateral support surface for housing corresponding rolling elements.
In both devices, when the third component is rigidly coupled to the second component, their combined rotation is opposed by the braking action of the viscous fluid. Conversely, when the third component can rotate freely with respect to the second component, no braking action is exerted on it by the viscous fluid present between the first and second components.
The aforementioned devices are relatively complex, since they require the assembly of a large number of components. In particular, their correct operation is dependent on the presence of a certain number of springs, associated with corresponding rolling elements in order to control the movement of the rolling elements in the housings in which they are placed.